The price of natural gas would need to nearly double for the plant to regain economic viability, according to Goodenough.

"If gas is trading at $1.90 or $2 per million BTU, and coal is trading at $4 per million BTU, a coal plant would need to get enough from its energy bid to recover for a $4 price, and gas is only $2," he said.

And we also get this chart:

So we seem to see that gas is cheaper than coal. That's great, so more gas fired plants will run than coal where there is a choice.

But that's not all there is to it. For gas is also more efficient than coal. That is, for whatever number of BTUs going into a plant we get more electricity out from a gas plant than a coal one:

The current stock of U.S. generation assets is not operating as efficiently as they could be, due largely to operational and economical issues. For example, the existing stock of coal plants is operating well below the efficiency of a new subcritical plant (10,410 versus 9,276 btu/kWh). If efficiency was the goal gas plants should run over coal plants (8,000 vs 10,400 Btu/kWh).

We seem to have 20% greater efficiency from gas plants than we do from coal. And that's not all we get either. We also get a reduction in greenhouse gas emissions:

The CO2 emissions from Natural Gas Combined Cycle (NGCC) plants are reduced relative to those produced by burning coal given the same power output because of the higher heat content of natural gas, the lower carbon intensity of gas relative to coal, and the higher overall efficiency of the NGCC plant relative to a coal-fired plant (1).

“The average emissions rates in the United States from natural gas-fired generation are: 1135 lbs/MWh (Mega Watt hours) of carbon dioxide, 0.1 lbs/MWh of sulfur dioxide, and 1.7 lbs/MWh of nitrogen oxides. Compared to the average air emissions from coal-fired generation, natural gas produces half as much carbon dioxide, less than a third as much nitrogen oxides, and one percent as much sulphur oxides at the power plant.”

Now we cannot add all of these together, this is obvious, because the lower emissions are already partly accounted for by the greater energy density of the gas which is already reflected in our per BTU price.

However, we can add up the following. The shale gas revolution has lowered, tremendously, the price of natural gas in the US. As it will do any and every where else that people are allowed to drill for it. In the process this will close coal plants as they find that they cannot compete with the pricing of that natural gas. That will lead to a halving, around and about, of emissions from that portion of the electricity system that is still fossil fuel fed.

There is more to it than this as well. Clean gas is an awful lot easier to achieve than clean coal. It's much, much, easier to strip the C out of CH4 before combustion than it is to collect, cool and compress CO2 from coal after combustion. So a move to gas would be at least a step towards that desired low to no carbon emission electricity generation system. There are energy losses in both cases but gas seems to have lower such as well.

Which leaves us with the real puzzle: just why are the hippies so against shale gas extraction when it's moving us in the right direction of beating climate change?